1. Field of the Invention
The invention relates generally to control apparatus for machines which assemble wooden rafters or the like and, more specifically, to a detection apparatus which will determine the presence or absence of a nailing plate at predetermined positions and affect control of the assembly apparatus to prevent further assembly if a required plate is missing or out of position.
2. Background of the Invention
The housing industry has moved toward greater use of pre-assembled components. These components, such as rafters or trusses, are assembled in a factory and shipped to the construction site. The use of pre-assembled components saves labor at the construction site, results in more uniform components and are less expensive to manufacture than stick-built components. The individual lumber elements of the rafters, trusses, or other components, are commonly secured to each other in the assembly of the building component by the use of connector plates with struck teeth. The connector plates are positioned in pairs opposite of each other on either side of the component being assembled. The connectors are positioned and then pressed into place in an assembly line process when they pass between a pair of rollers. Obviously, if one of the connecting plates is missing or is not in the appropriate position, the building component will not be assembled correctly and may not have the full designed strength or dimensions. There is a need, accordingly, to detect the proper positioning of the connector plates during assembly so as to avoid production of defective building components.